#include<stdio.h>
int fib(int n){
  int a=1;
  int b=1;
  int c=1;
  while(n>2){
  c=a+b;
  a=b;
  b=c;
  n--;
  }
  return c;
}
int main(){
int n=0;
int ret=0;
scanf("%d",&n);
 ret=fib(n);
printf("ret=%d\n",ret);
return 0;
}